merging

add mixin for some NSApplication constants

use calloc with ffi

libffi in 10.15+ has different usage (presumably for arm64)

arm64 has objc_sendMsg only

add missing headers

no more mach_override

remove unwanted objs

add missing function definitions

fiddle around with build settings

disable mach_override and grab the interpreter lock when performing respondsToSelector on a pike object

disable use of mach_override

fix some more leaks identified by the leaks tool

note that the free_svalue leak may not be an actual leak.

fix a bunch of memory leaks, correct Mapping wrapping caused by an "implicit" function definition

fixes for ffi calls on method dispatch: float param and return values in particular

fix memory leaks

add some setters

more bug fixes

more fixes for objective c 2

add option to skip stub building, and add another SDK location